Is there a way to safely reduce power output of a 6s battery to equal that of a 3s battery ?
Reason being I only have 3s esc two 6s lipos were giving to me

Yes, remove 3 cells. LOL.... Really, I have no idea without getting a power regulator.

Without changing to a smaller battery, use a lower KV motor.

Just need to make sure ESC can handle the voltage, I suspect his may be limited to 4S.

Someone who's skilled at soldering can possibly rewire a 6S pack into 2 separate 3S packs, but will need to buy balance leads for 3S and re-wire everything... lots of trouble to save a few bucks

Here's the wiring sequence for a 3S pack to get an idea of what needs to be done:
https://www.rcgroups.com/forums/show...0#post40111183